Humans today could be part Neanderthal, according to a new
study that found our ancestors interbred with an extinct hominid species some
millennia ago.

Neanderthals walked the Earth between about 130,000 and
30,000 years ago. While they co-existed with modern humans for a while,
eventually they went extinct and we didn't. There has been intense scientific
debate over how similar the two species were, and whether they might have mated
with each other.

"The issue has been highly contentious for some
time," said University of New Mexico genetic anthropologist Keith Hunley.

Last week at the annual meeting of the American Association
of Physical Anthropologists in Albuquerque, N.M., Hunley and colleagues presented
the results of a new study that found evidence for interbreeding between modern
humans and some other extinct ancient human species – either Neanderthals
(Homo neanderthalensis) or another
group such as Homo
heidelbergensis. The research was first reported by NatureNews.

The researchers looked at DNA samples from
humans living today, and found signs of leftover Neanderthal
genes introduced from this interbreeding. They looked at
genetic data from almost 2,000 people around the world, and calculated how much
genetic variation existed between samples. The results indicate that some
extinct group of hominids mixed their genes with ours at two points in history,
Hunley said.

One period of interbreeding probably occurred
shortly after Homo sapiens migrated
out of Africa around 60,000 years ago. The researchers found an excess of
genetic diversity in all modern people except Africans, suggesting that the
influx of Neanderthal-like DNA came after the exodus from Africa.

A second period of interbreeding is suggested
by the fact that the researchers measured even more genetic diversity among
people of Oceanic descent – people from Australia, New Zealand, New Guinea and
other Pacific islands.

"I think we show there's clear evidence
in the genome of living people of this mixture," Hunley told LiveScience. "The
fact that there's a clear signal implies that there was some significant
amount" of interbreeding, he said.

This work is the first time scientists have
used DNA from living people to look at this question, Hunley said.

In an earlier
study, Erik Trinkaus of Washington University in St.
Louis found suggestions of Neanderthal and modern human interbreeding by
comparing ancient bone fossils from the two species.

Trinkaus said the new work fits into his findings, though he
hasn't reviewed the details yet since Hunley's paper has not yet been published
in a peer-reviewed journal. "The conclusion makes
sense and fits with the majority of the data available," Trinkaus said.

"I have been arguing for this position throughout my
career, ever since I began to study Neandertals and other populations,"
said Milford Wolpoff of
the University of
Michigan. "It has always seemed clear that some Neandertal anatomy
appears in living populations."

Clara Moskowitz

Clara has a bachelor's degree in astronomy and physics from Wesleyan University, and a graduate certificate in science writing from the University of California, Santa Cruz. She has written for both Space.com and Live Science.